study of caspian sea river estuaries in guilan province base on benthic organisms

the coastal areas are highly productive system that is degrading due to receiving huge amount of various pollutants. despite of the important of north caspian sea estuaries the quality index of benthic fauna received less attention. in this survey the benthic population of 18 rivers estuaries in southern caspian sea were investigated. the benthic sampling and identification were conducted at eight points in each estuary in three periods of winter, spring and summer 2009. the shannon wiener diversity and the hilsenhoff biotic indices were used for evaluation of environmental quality. the result of shannon wiener index values in various rivers indicates that astara and lemir had the lowest and highest diversity respectively. the station 1 and 2 in river showed the lowest and offshore stations 5, 6 and 7 the highest diversity values. according to hilsenhoff biotic index for water quality classification, the stations of 1 and 2 with low quality were significantly difference with other stations. the quality of estuaries of khotbesara, navroud, heshmatrud and shirabad were strongly good and the other were slightly and moderately good condition. in generally, the quality of rivers in western region were better than the other regions, where they were characterized on the base of seasonal condition, biological properties of benthic fauna , morphology and watershed basin of the river.